Electrophotography – Cleaning of imaging surface – Plural diverse
Reexamination Certificate
2001-12-20
2003-10-28
Chen, Sophia S. (Department: 2852)
Electrophotography
Cleaning of imaging surface
Plural diverse
C399S071000, C399S350000
Reexamination Certificate
active
06640080
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image forming apparatus or an image forming method which is employed in copiers and printers.
BACKGROUND OF THE INVENTION
In recent years, in image forming apparatus to obtain high image quality at a high speed, an electrostatic latent image development system such as an electrophotographic system is almost exclusively employed. It is assumed that this trend will continue into the future. Therefore, it has been increasingly demanded to further improve image quality in said electrostatic latent image development system.
In the image forming apparatus employing an electrophotographic system, known as means to remove residual toner such as non-transferred toner and residual transferred toner on the photoreceptor are, for example, cleaning units employing a blade cleaning system in which a flat board-shaped cleaning blade, comprised of an elastic body, is brought into contact with the surface of the photoreceptor so as to remove said residual toner.
Cleaning blade holding systems in such cleaning units are mainly divided into a fixed holding system in which, for example, said cleaning blade is held employing a fixed type blade holder so that said cleaning blade is brought into pressure contact with the surface of the photoreceptor utilizing the elasticity of the blade itself, and a rotary holding system in which the cleaning blade is allowed to rotate around its axis, parallel to the rotational axis of the image holding body, and said cleaning blade is brought into pressure contact with the photoreceptor employing the action of a spring force or gravity. Among them, since it is possible to stably apply constant load to the photoreceptor over an extended period of time, those employing the rotary holding system are widely employed.
However, when the cleaning blade holding system is said rotary holding system, problems tends to occur such as so-called blade curl-under.
In recent years, from the viewpoint of achieving high image quality, a decrease in toner particle diameter has been demanded. Suitably employed as methods to prepare such toner particles have been polymerization methods such as an emulsion polymerization and a suspension polymerization method.
As a method to respond to said demand for further improvement of image quality, a decrease in particle diameter of the employed toner has been undertaken. However, as the particle diameter of said toner decreases, adhesive force such as van der Waals forces between said toner and the photoreceptor (in most cases, being an electrophotographic photoreceptor) increases compared to the weight of said toner. This fact results in a decrease in transfer efficiency of said toner onto the transfer material and a decrease in cleaning efficiency. As a result, the amount of toner which is not removed on said photoreceptor increases.
However, as the toner particle diameter decreases, adhesion force between toner particles and the photoreceptor increases. As a result, it becomes increasingly difficult to remove residual toner on the photoreceptor. Specifically, a so-called polymerization toner, which is prepared employing a polymerization method, is comprised of nearly spherical particles. The resultant toner particles roll on the photoreceptor, and pass under the cleaning blade. As a result, problems occur in which insufficient cleaning or insufficient residual toner removal tends to occur, whereby it becomes increasingly difficult to remove residual toner on the photoreceptor.
Said trend is more pronounced for the toner prepared employing a so-called polymerization method which is a suitable method to prepare toner particles having a minute diameter. When an emulsion polymerization method or a suspension polymerization is employed, toner particles are directly formed. As a result, in addition to the minute particle diameter, nearly spherical toner particles are formed, whereby the effective contact area between toner particles and the photoreceptor (hereinafter occasionally referred to as the electrophotographic photoreceptor or the photoreceptor) becomes large, and further, during cleaning, toner particles tend to roll on the surface of the photoreceptor. Due to that, “insufficient cleaning” occurs in which toner particles pass under the leading edge of the blade. On the other hand, in order to minimize such insufficient cleaning, when the cleaning member is excessively pressed onto the surface of the photoreceptor, the surface may be subjected to abrasion or toner particles are rubbed hard enough onto the surface to be crushed, whereby problems tend to occur on the surface of the photoreceptor. Said problems on the surface of the photoreceptor cause image problems such as white spots, white streaks, black spots, and black streaks. Accordingly, stable cleaning performance is not obtained over an extended period of time. As a result, when said problems are not overcome, it is impossible to achieve stable production of high quality images.
In order to minimize said insufficient cleaning, for example, Japanese Patent Publication Open to Public Inspection No. 3-179675 discloses a cleaning system in which mechanical cleaning and electrostatic cleaning are employed in combination.
Specifically, it is constituted in such a manner that a voltage applicable brush roller, comprised of conductive materials, is provided upstream from the cleaning blade with respect to the moving direction of the photoreceptor, and for example, a suitable bias voltage, having an opposite polarity of the residual toner on the photoreceptor, is applied to said brush roller. Thus, improvement of cleaning performance is attempted utilizing mechanical cleaning effects by the cleaning blade and electrostatic cleaning effects by the brush roller.
However, it is difficult to completely remove toner particles with a small particle diameter, and especially so are spherical toner particles which are prepared employing said polymerization method. Therefore, it has been demanded to develop a method to further enhance the cleaning performance. Further, in the image forming apparatus constituted as above, most residual toner on the photoreceptor is removed by the brush roller positioned upstream side respect to the moving direction of the photoreceptor. As a result, the amount of the residual toner, which reaches the cleaning blade, is frequently minimal. In such a case, frictional force on the photoreceptor increases so that blade curl-under as well as minute vibrations tend to occur. As a result, problems occur in which it becomes difficult to perform the stable production of high quality images over an extended period of time.
Furthermore, toner which is employed to visualize latent images formed on the photoreceptor is adhered to a wider area than the image forming area of the photoreceptor due to toner scattered by the development unit. Even though said cleaning system is employed, at present it is difficult to effectively remove the toner on the photoreceptor, which has been scattered over such a wide area.
In order to overcome such drawbacks, it has been considered to increase the cleaning area in the axis direction of the photoreceptor by increasing the width of the brush roller. However, when only the cleaning area is increased, the area, which is charged at a polarity opposite the residual toner, becomes excessively large due to the brush roller on the latent image holding member. As a result, in the opposite charge area which is charged by said brush roller and is not recharged by the charging unit, staining occurs due to toner adhesion as well as dielectric breakdown of the photosensitive layer of the photoreceptor. As a result, the apparatus interior tends to be stained and insufficient cleaning tends to occur.
Further, when the reversal development method, which is now mainly used in digital copiers, is employed, said problems are still more pronounced.
PROBLEMS TO BE SOLVED BY THE INVENTION
From the viewpoint of the foregoing, the present invention was achieved. An object of the present invention is to provide
Endo Isao
Yamada Hiroyuki
Chen Sophia S.
Konica Corporation
Muserlian Lucas and Mercanti
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